This invention pertains to a calibration apparatus for an analog-to-digital converter best suited for a waveform observing apparatus utilizing an analog-to-digital converter (hereinafter referred to as ADC) which is also known as a transient recorder.
An electrical signal waveform measurement instrument such as an oscilloscope or similar apparatus typically exhibits an overall measurement error in the range of several percent. The accuracy is primarily determined by acceptable tolerance for particular applications and by allowable circuit complexity and component tolerances.
In accordance with the present invention, a waveform observing apparatus known as a transient recorder utilizing ADC has been developed to store an analog signal to be observed after digitizing it for reproducing the waveform of all or part of the stored digital data. This enables one to process an analog signal digitally by using a computer. In such an apparatus, analog signal can be converted into a digital signal with .+-.0.4 to .+-.0.05% error by using a 7 to 10 bits high resolution ADC.
The aforementioned waveform observing apparatus is provided with signal attenuator and amplifier stages for accepting a wide voltage range of analog signal. If the input stage including such signal attenuator and amplifier is designed with circuits of essentially the same accuracy as that of a conventional oscilloscope, the overall accuracy of the entire ADC is as poor as several percent despite very high accuracy of the digital section. That is, the overall accuracy is far from fractions of 1 percent which can be achieved by ADC itself. High precision attenuator and amplifier are very complicated and also very expensive.
It is therefore one object of the present invention to provide a device which automatically reduces error of the input circuit and also the error of ADC itself to substantially equal to that of an ADC by simply adding a simple circuit even if an input stage circuit of similar accuracy to conventional circuit may be used.
Other objects and attainments of the present invention will become apparent to those having ordinary skill in the art upon a reading of the following description when taken in conjunction with the accompanying drawings.